Positive position interlock concealment shutter

ABSTRACT

A positive position interlock concealment shutter - for preventing the accidental or intentional actuation of a concealed interlock switch in a microwave oven when its door is in the open position - comprises a moveable metal plate having an aperture therethrough which can be aligned with the conventional aperture in the oven face. The position of the plate and its aperture is controlled by a door guide arm which includes a camming surface. The slope of the cam surface is designed to allow sufficient door movement for the latch pawl or the door pin to clear the shutter aperture during door opening before shutter closing occurs. The cam surface is such that the shutter closes before access to the interlock becomes possible. The return of the shutter to the open position upon the closing of the door may be spring controlled.

Robinson et al. Aug. 5, 1975 [541 POSITIVE POSITION INTERLOCK 3,715,552 2/1973 Umezu et a1. 219/1055 C CONCEALMENT SHUTTER 3,748,423 7/l973 Haagensen 219/1055 D 3,750,643 8/1973 Fowler l26/l97 [75] Inventors: Earl W. Robinson, Rockville, Md.;

i g z zg gzfizz g fg j i Primary E.raminerBruce A. Reynolds Bel'tsvme M d. Attorney, Agent, or FirmBrowdy and Neimark 73] Assi nee: The United States of America as g represented by the Secretary of the [57] ABSTRACT Department of Health, Education, A positive position interlock concealment shutter and welfare Washington, for preventing the accidental or intentional actuation [22] Filed. May 21 1974 of a concealed interlock switch in a microwave oven when its door is in the open position comprises a PP NOJ 4711999 moveable metal plate having an aperture therethrough which can be aligned with the conventional aperture 52 us. c1 219/1055 c; 49/73; 126/197; in the feee- The POsition 0f the Plate and its 2O0/50 A; 219/1055 D erture is controlled by a door guide arm which in- 51 Int. c1. H05b 9/06 eludes e eammihg surface The SlePe the eam [58 Field of Search ..219/10.55 c, 10.55 D, face is designed ehew sufheieh deer mevemem fer 219/1055 E, 10.55 R; 200/50 A, 50 AA the latch pawl or the door pin to clear the shutter ap- 200/61.62; 126/197; 49/449, 67, 73, 114 erture during door opening before shutter closing oc- 49/119, 122, 303 0 ours. The cam surface is such that the shutter closes before access to the interlock becomes possible. The [56] References Cited return of the shutter to the open position upon the UNITED STATES PATENTS Johnson t. ZOO/61.62

closing of the door may be spring controlled.

5 Claims, 4 Drawing Figures PATENTEDAUB 51915 3,898,412

SHEET 1 FIG. 2

PATENTED AUG 51975 SHEET FIG. 3

FIG. 4

POSITIVE POSITION INTERLOCK CONCEALMENT SHUTTER FIELD OF THE INVENTION The present invention relates to an interlock concealment shutter for microwave ovens or other mechanisms for which the use of a concealed safety interlock switch BACKGROUND OF THE INVENTION Microwave cooking devices heat and cook food through the utilization of electromagnetic energy at frequencies of 915 mI-Iz and 2450 mI-Iz. Because of the danger of radiation damage to human tissue it is necessary to prevent leakage of microwave energy above safe levels from the cavity. For those devices classified as microwave ovens under P.L. 90.602, 21 CFR Subchapter J 1030.10 limits of allowed leakage have been prescribed by law. The law also requires the use of two interlock switches to prevent access to the cavity while the oven is generating microwave energyand in addition requires that one interlock be concealed.

A forthcoming amendment to the regulations to be effective Aug. 6, 1974 will add the further explicit requirement that each of the two required interlocks cause generation of microwave energy to cease prior to the time when emission will exceed the prescribed limits upon unlatching oropening of the oven door.

Prior art devices failed to provide an adequate degree of concealment in combination with the necessary actuation sensitivity to meet the forthcoming emission limits.

SUMMARY OF THE INVENTION The principle object of the present invention is to provide a positive position interlock concealment shutter which in conjunction with one interlock provides a high degree of concealment and which, in conjunction with one other unconcealed interlock, allows the oven to meet all present and proposed requirements of the performance standards of microwave ovens (21 CFR 1030.10) for microwave emission.

Another object of the present invention is to overcome the defects of the prior art, such as indicated above.

A further object is to provide an interlock concealment shutter for microwave ovens or any other mechanism requiring the use of a concealed interlock safety switch.

Yet another object of the present invention is to provide a safety device for microwave ovens which prevents the supply of energy to the oven cavity whenever the oven door is in the open position.

Still another object is to provide a device for preventing access to an interlock switch after any door movement from the closed position in excess of the minimum necessary to let the latch pawl or actuating pin clear the opening in the oven face.

In furtherance of these and other objects, a principal feature of the instant invention is a moveable plate or shutter whose closed position is positively controlled. Another feature is a door guide arm including a camming surface for forcing the shutter to close as an appropriate amount of door motion occurs.

The concealed interlock shutter of the present invention is characterized by a moveable metal plate located behind the oven face including an aperture which can be aligned with a similar aperture in the oven face. The position of the moveable plate is controlled by means of a camming surface on a door guide arm so that access to the interlock switch is prevented after any door movement from the closed position in excess of the minimum necessary to allow the latch pawl or actuating pin to clear the opening. The return of the shutter to the open position upon the closing of the door may be spring controlled, or could be made positive by means of suitable rollers and/or a slotted guide arm. The movement of the shutter to the closed position must be positive and cannot be spring controlled. The shutter opening, length of the shutter beyond the opening, the shutter stop and the door guide shape are designed such that any over travel of the shutter will not expose the interlock switch. I

For a better understanding of the invention, a possible embodiment thereof will now be described with reference-to theattached drawing, it being understood that the embodiment is merely exemplary.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a partially cutaway perspective view of one embodiment of the interlock concealment shutter with the microwave oven door in a closed position.

FIG. 2 is a partially cutaway perspective view of the interlock concealment shutter of FIG. 1 with the microwave oven door in the open position.

FIG. 3 is a partially cutaway plan view of the interlock concealment shutter of FIG. 1.

FIG. 4 is a partially cutaway plan view of the interlock concealment shutter of FIG. 2.

DETAILED DESCRIPTION Referring now to FIGS. 1 and 3, there is shown a microwave oven 10, having a front oven face or wall 12 and an oven door 14 pivotably mounted adjacent thereto. A latch pawl 16 mounted on the side of the door 14 adjacent to the front oven face 12 engages an interlock switch 18 mounted on the interior side of the front oven face 12 through an aperture 34 therein (see FIG. 3). A shutter assembly 20 comprises a plate-like shutter 36 made of metal or any other suitable material and mounted on the interior surface of the front oven face 12. When the oven door 14 is closed, the shutter 36 is opened and an aperture 40 in the shutter 36 is aligned with the aperture 34 in the front oven face 12 (see FIG. 3).

A door guide arm 22 made of metal or any other suitable material .is pivotably mounted from the door 14 by a guide pivot 42 (see FIG. 3) which is integral with the oven door 14. The door guide arm 22 which extends through a slot 38 in the front oven face 12 into the interior of the microwave oven 10, includes cam surfaces 44 and 46 which are engaged by a fixed door guide roller 26 and a shutter control roller 24, respectively. The fixed door guide roller 26 is mounted in a fixed position within the microwave oven chamber by any suitable means (not shown) connected to a stationary part of the oven, while the shutter control roller 24 is fixedly mounted atop a platform 48 integral with the sliding surface 36. A shutter stop 32 is mounted on the interior side of the front oven face 12 to prevent overtravel of the shutter 36 and the consequent exposure of the interlock switch 18. Any suitable type of shutter guide (not shown) may be utilized to guide the shutter 36 along the desired path of travel and to-maintain the shutter 36 in sliding abutment with the front oven face 12. I

A shutter return spring 28 may be employed to return the shutter 36 to the open position upon 'closing of the door 14. Alternatively, the return of the shutter 36 to the open position may be accomplished by means of suitable additional rollers and/or a slotted door guide arm. Also, a door guide spring 30 may be employed to facilitate the guidance of door 14 during the opening and closing thereof.

The operation of the instant invention will now be de-' scribed with reference to FIGS. 2 and 4, which show the oven door 14 partially opened and the shutter assembly 20 in a closed position, i.e. with the oven face aperture 34 being blocked by the end portion 52 of shutter 36. As the door 14 is opened, the camsurfaces 44 and 46 remain in contact with the fixed door guide roller 26 and the shutter control roller 24, respectively. As the high point 50 of the cam surface 46 approaches the shutter control roller 24, the shutter 36 is moved in the direction of the shutter stop 32. The movement of the shutter 36 causes the shutter aperture 40 to become misaligned with the front oven face opening 34. Therefore, as the door is opened, the end portion 52 of shutter 36 blocks the front oven face aperture 40 and,.

thereby prevents access to the interlock switch 18 except when the door 14 is slightly ajar orcompletely closed. As discussed hereinabove,- the shutter return a concealed interlock switch located in the interior of a high frequency energy emitting device by any part of the human bodyor by tools or objects commonly found in the household; including but not limited to screwdrivers, pencils, toothpicks and wire; without the need for disassembling the device or removing its housing.

Thus, the foregoing description of the specific embodiment will so fully reveal the general nature of the invention that others can, by applying current knowledge, readily modify such specific embodiment and/or adapt it for various applications without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiment. Further, it is to be understood that the phraseology or terminology employed 4 herein is for the purposeof description and not of limitation. i I

What is claimed is: Y 1

l. A positive position interlock concealment shutter forpreventing the accidental or intentional actuation of a concealed interlock switch located in the interior of a'high frequency energy utilization device having a latch pawl mounted on a door of the device and engaging theinterlock switch through a first aperture in a front wall of the device comprising:

a shutter assembly mounted substantially adjacent to and in sliding relationship with the interior side of the front wall of the device, said shutter assembly including a first roller connected thereto, a second aperture aligned with said first aperture in the front wall of the device when the door thereof is closed anda solid body portion adjacent to said second aperture, 1,

a second roller fixedly mounted within the interior of the device; i i

a doorjguidea'rm attached 'to the door of the device and extending into the interior of the device through a third aperture in the front wall of the device, said guide 'arm including cam means movable over said first and second rollers for controlling the position of said shutter assembly and said second aperture therein in such a manner as to permit sufficient door movement for the latch pawl to clear said second aperture in said shutter assembly during the opening of the door and such that said second aperture in said shutter assembly is misaligned with said first aperture and said solid portion of said shutter assemblyis aligned with said first aperture in the front wall of the device as the door thereof is opened, whereby access to the interlock switch is prevented by said solid portion of said shutter assembly. 7

2. The device of claim 1 further comprising a shutter stop means mounted on the interior side of the front wall of the device in the path of travel of said shutter assembly for preventing the overtravel thereof.

3. The device of claim 1 wherein said shutter assembly includes a platform means integral therewith and extending toward the interior of the device for mounting said first roller. g

4. The device of claim 1 further comprising spring means connected to the interior side of the front wall of the device and to said shutter assembly for realigning said second aperture in said shutter assembly with said first aperture in the front wall of the device upon the closing of the door thereof.

5. The deviceof claim 1 further comprising spring means connected to said door guide arm and to an interior portion of the device for facilitating the guidance of the door thereof.- 

1. A positive position interlock concealment shutter for preventing the accidental or intentional actuation of a concealed interlock switch located in the interior of a high frequency energy utilization device having a latch pawl mounted on a door of the device and engaging the interlock switch through a first aperture in a front wall of the device comprising: a shutter assembly mounted substantially adjacent to and in sliding relationship with the interior side of the front wall of the device, said shutter assembly including a first roller connected thereto, a second aperture aligned with said first aperture in the front wall of the device when the door thereof is closed and a solid body portion adjacent to said second aperture; a second roller fixedly mounted within the interior of the device; a door guide arm attached to the door of the devIce and extending into the interior of the device through a third aperture in the front wall of the device, said guide arm including cam means movable over said first and second rollers for controlling the position of said shutter assembly and said second aperture therein in such a manner as to permit sufficient door movement for the latch pawl to clear said second aperture in said shutter assembly during the opening of the door and such that said second aperture in said shutter assembly is misaligned with said first aperture and said solid portion of said shutter assembly is aligned with said first aperture in the front wall of the device as the door thereof is opened, whereby access to the interlock switch is prevented by said solid portion of said shutter assembly.
 2. The device of claim 1 further comprising a shutter stop means mounted on the interior side of the front wall of the device in the path of travel of said shutter assembly for preventing the overtravel thereof.
 3. The device of claim 1 wherein said shutter assembly includes a platform means integral therewith and extending toward the interior of the device for mounting said first roller.
 4. The device of claim 1 further comprising spring means connected to the interior side of the front wall of the device and to said shutter assembly for realigning said second aperture in said shutter assembly with said first aperture in the front wall of the device upon the closing of the door thereof.
 5. The device of claim 1 further comprising spring means connected to said door guide arm and to an interior portion of the device for facilitating the guidance of the door thereof. 